972 
FXUS64 KBMX 081145
AFDBMX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BIRMINGHAM AL
645 AM CDT SAT SEP 8 2012

.UPDATE...
FOR 12Z AVIATION.

&&

.DISCUSSION...

BIG CHANGES ARE IN STORE FOR CENTRAL ALABAMA OVER THE NEXT 24
HOURS. MUCH DRIER AIR AND COOLER TEMPERATURES ARE ON THE WAY...BUT
BEFORE THEY GET HERE...WE'VE GOT ONE MORE SYSTEM TO DEAL WITH.

A LONGWAVE TROUGH IS PARKED OVER THE EASTERN THIRD OF CANADA THIS
MORNING AND BEFORE IT RETREATS FURTHER OFF TO THE NORTH...TWO MORE
SHORTWAVE TROUGHS WILL AFFECT US AS THEY ROUND THE SOUTHERN
PERIPHERY OF THE LARGER TROUGH. THE FIRST IS THE ONE RESPONSIBLE
FOR THE APPROACHING COLD FRONT THIS MORNING. PREFRONTAL ACTIVITY
HAS BEEN ONGOING AHEAD OF THE COLD FRONT FOR THE LAST 6-10
HOURS...CREATING A LINE OF SHOWERS AND THUNDERSTORMS WHICH HAS
BEEN WEAKENING SINCE MIDNIGHT. THIS PRECIPITATION IS ON OUR DOOR
STEP AT FORECAST TIME...AND THE QUESTION IN THE SHORT TERM WILL
BE...HOW MUCH MORE ACTIVITY WILL WE SEE TODAY AS THE FRONT MOVES
THROUGH THE AREA. CURRENTLY STRETCHING FROM ARKLATEX NEWD INTO THE
GREAT LAKES...THE FRONT IS EXPECTED TO CLOSE IN ON CENTRAL ALABAMA
THROUGH THE MORNING HOURS. MODELS ARE PRETTY CONSISTENT WITH A
COUPLE OF THINGS. FIRST...HAVING THE FRONT APPROACHING THE I-20
CORRIDOR AROUND THE NOON HOUR TODAY...AND SECOND...THE IDEA OF
POST FRONTAL SHOWERS. MY THOUGHTS ARE THAT BECAUSE THE PARENT LOW
IS SO FAR OFF TO THE NORTH AND THERE REALLY ISN'T A WHOLE LOT OF
SYNOPTIC SUPPORT FOR ORGANIZED CONVECTION...IT WILL TAKE THE
DIURNAL HEATING OF THE DAY TO HELP CREATE THE NECESSARY INSTABILITY
FOR THUNDERSTORMS. BECAUSE OF THIS...THE MAIN AREA OF FOCUS FOR
THUNDERSTORMS THIS AFTERNOON WILL BE ALONG AND SOUTH OF INTERSTATE
20. THE GOOD NEWS IS...AS I SAID BEFORE... THERE ISN'T A WHOLE LOT
OF SYNOPTIC SUPPORT. THIS MEANS THERE WON'T BE MUCH IN THE WAY OF
SHEAR TO SUSTAIN UPDRAFT GROWTH. 0-6KM BULK SHEAR OF 20-25 KTS
AHEAD OF THE FRONT IS ABOUT ALL THIS SYSTEM LOOKS TO MUSTER ACROSS
OUR AREA...AND THIS SHOULD CURB ANY CONCERNS ABOUT SEVERE WEATHER.
POST FRONTAL SHOWERS WILL BE POSSIBLE THROUGH THE AFTERNOON...BUT
WILL BE OF LITTLE CONSEQUENCE.

THE SECOND OF THE TWO SHORTWAVE TROUGHS WILL ROUND THE BASE OF THE 
LONGWAVE TROUGH TONIGHT...AND THIS WILL BE THE INSTIGATOR IN KEEPING 
THE FRONT MOVING THROUGH THE STATE.  RAIN SHOULD END FROM NORTHWEST 
TO SOUTHEAST AFTER SUNSET THIS EVENING AND DRY AIR WILL REPLACE THE 
RAIN FAIRLY QUICKLY.

THE NEXT QUESTION WILL BE HOW COOL WILL IT GET TONIGHT.  LOOKING 
UPSTREAM...POST FRONTAL DEW POINTS IN THE UPPER 40S AND LOW 50S ARE 
FAIRLY PREVALENT IN THE MID-MISSISSIPPI VALLEY.  I DON'T THINK WE 
WILL SEE DEW POINTS IN THE 40S...BUT LOW TO MIDDLE 50S WILL BE QUITE 
POSSIBLE...AND THIS WOULD LEAD TO UNSEASONABLY COOL TEMPERATURES FOR 
SUNDAY MORNING.  HAVE GONE AHEAD AND DROPPED TEMPERATURES A BIT FROM 
PREVIOUS FORECAST PACKAGES AND THOUGH NOT EVERYONE IS EXPECTED TO 
DROP INTO THE LOW TO MIDDLE 50S...A LARGE PORTION OF OUR NORTHERN 
COUNTIES WILL.

THE REST OF THE FORECAST HAS US DOMINATED BY HIGH PRESSURE ALOFT AND 
AT THE SURFACE.  THIS MEANS DRY CONDITIONS ALL WEEK AND BELOW NORMAL 
TEMPERATURES CAN BE EXPECTED SUNDAY THROUGH TUESDAY...WITH A SLIGHT 
WARMING TREND THROUGHOUT THE WORKWEEK.

27

&&

.AVIATION...
12Z TAF DISCUSSION.

LOW CONFIDENCE FORECAST FOR TIMING OF SHOWERS/STORMS BEFORE FRONTAL 
PASSAGE. THE LINE OF STRONG STORMS AHEAD OF THE FRONT ACROSS THE MID 
MISSISSIPPI VALLEY LATE YESTERDAY DISSIPATED INTO A FEW SHOWERS AS 
IT MOVED INTO NW AL EARLY THIS MORNING. BELIEVE THAT THERE WILL BE 
ADDITIONAL DEVELOPMENT AS WE GO THRU THE DAY AND ANOTHER LINE OF 
SHOWERS/STORMS COULD DEVELOP BY AFTERNOON...BUT IT WILL BE VERY 
DIFFICULT TO PIN DOWN EXACT TIMING OF ANY IMPACTS TO THE TERMINALS 
SINCE THERE IS CURRENTLY NOT A DEFINITE FEATURE THAT CAN BE 
TRACKED...OTHER THEN THE FRONT ITSELF. FOR NOW HAVE GONE WITH VCSH 
FOR THE NORTHERN SITES WITH A TEMPO FOR SHRA JUST AHEAD OF THE 
FRONT...THEN SOME LIGHT POST FRONTAL SHOWERS BEFORE CLEARING OUT 
LATE AFTN/EARLY EVNG. FOR THE SOUTH...THINK THEY WILL HAVE THE BEST 
SHOT AT SEEING ANY TS DEVELOPMENT THIS AFTN BEFORE THE FRONT MOVES 
THRU. TIMING OF SHRA/TS WILL LIKELY HAVE TO BE ADJUSTED AS WE GO 
THRU THE DAY BASED ON HOW THE SYSTEM EVOLVES AND ITS SPEED.

SOUTHWEST WINDS OF 5-7 KTS WILL QUICKLY SHIFT TO THE NORTHWEST 
BEHIND THE FRONT. POST FRONTAL WINDS WILL BE AROUND 10 KTS WITH SOME 
POSSIBLE GUSTS UP TO 18 KTS IN THE NORTH...WITH SLIGHTLY LOWER WINDS 
IN THE SOUTH. WINDS SHOULD THEN DECREASE LATE IN THE EVENING.

19

&&

.PRELIMINARY POINT TEMPS/POPS...
GADSDEN     81  54  81  53  83 /  70  10   0   0   0 
ANNISTON    83  55  82  55  83 /  70  10   0   0   0 
BIRMINGHAM  84  55  82  58  83 /  70  10   0   0   0 
TUSCALOOSA  86  57  84  56  85 /  70   0   0   0   0 
CALERA      84  57  82  58  84 /  70  10   0   0   0 
AUBURN      88  61  85  59  85 /  70  30   0   0   0 
MONTGOMERY  89  62  86  58  87 /  70  30   0   0   0 
TROY        89  62  85  54  86 /  60  30   0   0   0 

&&

.BMX WATCHES/WARNINGS/ADVISORIES...
NONE. 

&&

$$

27/19